Abnormalities of chromosome band 13q14 occur in hematologic malignancies of all lineages and at all stages of differentiation. We showed the presence of myeloid- and lymphoid-specific breakpoint cluster regions within chromosome band 13q14 in acute leukemia (Genes Chromosome Cancer 25:222-229, 1999). We established a new cell line from one of the lymphoid cases, MUTZ5, that carries a single t(12;13) translocation (Leukemia 15:1471-1474, 2001). The molecular characterization of this translocation allowed us to identify a new gene called FLJ13639 that is disrupted and lost in the MUTZ5 cell line. This gene shares homologies with the large family of short-chain dehydrogenase reductase (SDR). This new protein localizes in the mitochondria. One of the consequences of the loss of FLJ13639 is the over-expression of CD24. CD24 over-expression has been linked with hypoxic conditions and poor prognostic in acute leukemia as well as chemoresistance. We therefore hypothesize that loss of the FLJ13639 expression leads to altered mitochondrial function as well as increase in CD24 expression that provides leukemia cells with a proliferation and invasiveness advantage as well as a certain degree of resistance to chemotherapy. The addition of exogenous FLJ13639 recombinant protein would lead to an increase in chemosensitivity and reduce chemoprotection provided to leukemia cells by altered mitochondrial function and over-expression of CD24, among other markers. Our three hypothesis-driven Specific aims will be as follows: Specific Aim 1: Hypothesis: The FLJ13639 gene is down regulated in acute leukemia by both genetic and epigenetic events;Specific Aim 2: Hypothesis: The FLJ13639-P1 protein has a dehydrogenase activity and is involved in electron transport in mitochondria and Specific Aim 3: Hypothesis: Delivery of FLJ13639 protein induces apoptosis in acute leukemia cells. Confirmation of the role of the loss of FLJ13639 in leukemia prognosis, increase of chemo resistance should lead us and others, to develop new prognostic tools as well as novel, innovative therapeutic strategies.